Valve-operating mechanism



- March 19, l929- a, A. IP. BRUSH ET Ax. 'l

liatented Mar. 19, e

UNITED STATES PATENT oFFlcE.

ALANSON I. BRUSH AND OWEN M. NACKER, OF DETROIT, MICHIGAN.

VALVE-OPERATING MECHANISM.

Application filed March 12, 1921. Serial No. 451,712.

The invention relates to valve-operating mechanism of that type in which oppet valves are actuated by cams through tie lmedium of tappets. It is the object of the invention to obtain a construction which will permit of'setting of the operating mechanism without any dangerl of the riding of the valve or failure to completely engage its seat. To this'end the invention consists; first, in the peculiar' construction of the cam, and; second, in various features of construction as hereinafter set forth.

Thedrawing represents the valve operating mechanism in sectional elevation.

In the construction of cams for operating valve tappets, there is first a base circle from which the lifting portion of the cam rises as a rectilinear or curvilinear tangent to this circle. In the setting of the tappets it is necessary to provide a certain amount of clearance or backlash, as otherwise there is danger 0f holding the valve olf of its seat, especially where expansion takes place in the parts due to the heat of the engine. On the other hand, this clearance is a source of noise and is otherwise objectionable'so that it is desirable to reduce the same to the minimum. improved construction the cam is formed with the lifting portion tangent to a 'segment of the base circle, but with a clearance below the base circle for the greater portion of the travel of the cam while the valve is engaging its seat. This construction permits of setting of the tappets so that there is practically no clearance from the base circle without, however, endangering the riding of the valve, for the dwell upon the base circle is short and adjacent to the seating portion of the cam and abundant clearance is provided for the great-r er part of the travel.

lIVith a cam constructed as described, if used with the usual cooperating parts, would be noisy, for the cam engaging roller would drop against the clearance portion of the cam, while the re-engagement with the lifting por? tion of the cam would cause a striking of the tappet. Such a result we have avoided' by resiliently holding the cam-engaging rider from thus dropping, so that its movement will be limited by that required to permit the full seating of the valve. As shown, We employ a spring of lighter tension than the valveoperating spring, which operates to hold the cam rider in constant contact with the tappet.

With our In the construction as specifically shown, F isthe push rod, and Gr the rocker arm which engages the rod F and carries the roller H forfv engagingv the actuating cam I. The cam I is constructed as before described with a lifting portion J, .which is tangent to segments of the base circle, said segments being of a limited angle, preferably not to exceed ten degrees and shown in the drawings as included between the limiting radii KK and KK.

L is the clearance portion of the cam which is cut below the base circle'andconnects with the segments KK and KK by inclined portions M and MT. The rocker Gr is held in contact with the rod F by a spring N, which springis of less tension than the spring, not shown, for closing the valve against its seat so as not to interfere with the seating of the valve, but is sufficient in tension to hold said rocker from dropping into the clearance space of the cam.

Vith the construction as described, in originally setting the valve mechanism it may be adjusted until all noise -is eliminated. This may result in the riding of the valve during vthe interval in which the roller H is in conbase circle and of a larger angular magnitude;

2. A cam for valve operating mechanism of internal combustion engines comprising a lifting portion, base circle segments on opposite sides of said lifting portion and to which it is tangent, said segments being of limited angular magnitude but suflicientto arrest movement of the follower and a clearance portion of lesser radius than said base circle between said segments.

y In testimony whereof we affix our signatures.

ALANsoN P. BRUSH. ownN M. NAcKns. 

